Vaccination is one of the most cost-effective strategies for conferring immunity against a host of preventable diseases. The World Health Organization estimates that over 2.5 million child deaths are prevented annually worldwide due to vaccination efforts, however, an estimated 24 million children under the age of one are not reached by immunization programs. Infants must receive all recommended vaccinations in a timely manner to be fully protected from deadly infectious diseases such as tuberculosis, diphtheria, pertussis and polio. A large body of evidence has shown that children in socio-economically disadvantaged backgrounds are more likely to be vaccinated late, or not at all, compared to their counterparts from wealthier and more educated families, leaving them susceptible to preventable illness. While Tanzania has successfully achieved high national vaccination coverage, substantial regional variation exists and intermittent vaccination campaigns have masked poor rates of vaccination timeliness. In this proposal we seek to evaluate the feasibility and utility of combining two emerging types of interventions - mobile health (mHealth) and conditional cash transfers - to overcome individual barriers to timely vaccinations. Researchers at Duke University's Global Health Institute and Tanzania's National Institute of Medical Research (NIMR), in collaboration with Tanzania's Expanded Programme on Immunisations (EPI), will partner to evaluate whether an mHealth-supported scheduling, reminder, and tracking system, combined with an innovative multi-tiered financial incentive scheme for families with young children, is acceptable and effective in improving rates of vaccination coverage and timeliness. The specific aims of the proposal are to (1) conduct formative research to identify locally relevant barriers to timely vaccinations; (2) develop an mHealth system to facilitate and monitor timely vaccinations and conduct surveys with 400 late-stage pregnant women in which contingent valuation methods are used to identify incentive amounts that vary systematically with the value of barriers to timely vaccinations, and (3) assess the efficacy of the intervention consisting of mHealth reminders and multi-tiered conditional cash transfers (CCT) for improving the rates and timeliness of vaccinations among infants in their first 6 months of life. Qualitative follow-up surveys with a subset of women will assess barriers to the acceptability and scalability of this mHealth-CCT intervention. The study will be implemented with support from Tanzania's Ministry of Health and Social Welfare. Study results will form the basis for a pragmatic randomized controlled trial of the efficacy and cost-effectiveness of mHealth reminders and multi-tiered conditional cash transfers as means of improving timely vaccinations of young children.